Advanced nuclear reactor systems, such as the Westinghouse AP600 reactor, General Electric Small Boiling Water Reactor, and other new reactor concepts such as the Multi-Application Small Light Water Reactor (MASLWR) rely on primary system depressurization as a key safety function. Usually power operated valves or squib valves are used for this purpose. These valves have to be actuated by an electric signal which is a result of electronically processed sensor signals. These valves are not passive in their operation and are prone to failure of mechanical actuators, loss of power sources and failure of sensors and of signal processing systems. Another disadvantage of conventional valves results from the use of springs to maintain the valve in the closed position. Springs tend to fatigue after long-term compression, thereby impairing the accuracy of the valve.